Motor-driven power steering apparatus

ABSTRACT

A generator generates two voltage outputs which have different voltage levels. One voltage output from the generator is used for operating a power steering apparatus. Another voltage output from the generator is used for charging a battery which supplies current to other loads.

FIELD OF THE INVENTION

The present invention relates to a power steering apparatus whichdepends on DC power as an energy source for generating an auxiliarysteering force; and more specifically, the present invention relates tomotor-driven power steering apparatus which is profitable for apassenger car using a DC motor as an actuator for generating anauxiliary steering force.

BACKGROUND OF THE INVENTION

A conventional power steering apparatus comprises a motor for generatingan auxiliary steering force, a control apparatus for regulating currentof the motor corresponding to the steering force, and a battery as acurrent source, for instance, as disclosed on FIG. 1 of Japanese PatentLaid-Open No. 59-156863 (1984), published on Sept. 6, 1984, and entitled"Power Steering Apparatus of Automobile".

The apparatus of the prior art uses a standard battery which is used inthe automobile as a current power source for all electric devicesthereof. However, the standard battery does not have the function ofproviding an output corresponding to the current value of the load ofthe automobile.

On the other hand, a generator for charging batteries which has twoarmature windings connected in star connection, respectively, forgenerating two similar voltages is disclosed in FIG. 3 of the U.S. Pat.No. 4,045,718, entitled "Multiple Winding Multiple Voltage AlternatorElectrical Supply System". However, the prior art discloses that theconnection of these windings to the load is not carried out,respectively, and these two windings are the same in electricalstructure.

In the conventional power steering apparatus sufficient consideration isnot given to the large current consumption of the motor for generatingan auxiliary steering force and the affect thereof an other electricalsystems in the vehicle. Especially, the conventional power steeringapparatus has a drawback in that the illumination provided by theheadlights of the automobile is reduced and the electrical devicesmounted on the vehicle, such as lights, wiper, and air-conditioner, etc.are undesirably influenced by the steering of the wheel at night whenthe automobile stops or while the engine is idling.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a motor-driven powersteering apparatus which can operate properly without exerting a badinfluence upon other electrical devices which use the same battery inthe automobile.

The object of the present invention is attained in such a manner thattwo different DC voltages are output from a generator driver by theengine which is equipped for charging at least one battery, one DCvoltage from the generator being supplied to the power steering, whilethe other DC voltage therefrom is supplied to a battery used for otherelectrical devices mounted on the automobile.

According to the present invention, since separate DC voltages aresupplied from different electric power systems to the power steeringsystem and to the other devices in the electrical system, respectively,the other electrical devices are not affected by the operation of thepower steering apparatus. And further, since the supplied voltage to thepower steering system can be increased without being affected by otherelectrical apparatuses mounted on the automobile, the operation of thepower steering system can be reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the first embodiment of the present invention;

FIG. 2 shows a sectional view of the generator applied to the presentinvention;

FIG. 3 is a circuit diagram of the generator shown in FIG. 2;

FIG. 4 shows the second embodiment of the present invention;

FIG. 5 shows the third embodiment of the present invention;

FIG. 6 is a circuit diagram of the third embodiment shown in FIG. 5;

FIG. 7 is a diagram for explaining the operation of the circuit shown inFIG. 6 when a predetermined voltage is obtained from the generator byrotation of the engine;

FIG. 8 is a diagram for explaining the operation of the circuit shown inFIG. 6 when the engine stops; and

FIG. 9 shows the 4th embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a steering shaft 1A, which is rotatable freely bythe steering wheel 1, is connected to a gear box 4 of a gear rack 5through an universal joint 2. The rotating force of the steering shaft1A is transmitted to the gear rack 50 through the gear box having apinion gear (not shown) which is rotated by the universal joint 2.

A torque detector 3 is mounted on the gear box 4 for detecting thetorque of the steering shaft 1A. The detected output of the torquedetector 3 is input to a controller 10.

A tie rod 7 is connected to the respective ends of the gear rack 5. Thesteering of the wheel 8 takes place by the operation of the gear rack 5and the tie rod 7, as is well known.

A gear box 6 of the gear rack 5 is connected to a motor 11 through areducer 20. The motor 11 is driven by a control signal of the controller10.

A pulley 14 is fixed on the rotational axis of the engine 13. A pulley16 is fixed on the rotational axis of a generator 17. A belt 15 issuspended between the pulley 14 and the pulley 16. The generator 17 hasfirst output terminals 21 and the second output terminals 22. Batteries9 and 18 are connected to these output terminals 21 and 22,respectively. The controller 10 is connected to the output terminals ofthe battery 9. Most other electrical loads 12 of the vehicle areconnected to the output terminals of the battery 18.

When the steering wheel 1 is operated, the torque detector 3 detects thetorque of the steering shaft 1A to input a detecting signal to thecontroller 10. The motor 11 is driven by a control signal from thecontroller 10, and gives the auxiliary steering force to overcome theroad surface friction generated between the wheel 8 and the roadsurface.

Referring to FIG. 2, the generator 17 outputs a first DC output voltageA of a comparatively low voltage for charging the battery 18 of 12 voltsand supplying electric power to the various kinds of loads 12, and asecond DC output voltage B of a comparatively high voltage (48 volts)for driving the motor 7 of the power steering system. The generatorcomprises two sets of armature windings 112 and 113 and two sets ofrectifiers (diodes) 115 and 117. Other than that, the generator isalmost the same as a standard generated (called an AC dynamo). Thepulley 16 is connected to the shaft 101 which is suspended by two setsof bearings 107. The rotor is formed by the iron core 102 of rundleconfiguration and the field winding 103 is mounted on the shaft 101.

The field winding 103 is connected to the outside through a slip ring104 and a brush 105. A predetermined exciting current is supplied from avoltage regulator (not shown). As a result, a three-phase AC voltage isgenerated by the armature windings 112 and 113 when the engine 13 isdriven. The three-phase AC voltage is supplied to the rectifiers 115 and117 through lead wires 114 and 116. First and second DC voltages aregenerated at the terminals A₁ and A₂ of the rectifier 117 and theterminals B₁ and B₂ of the rectifier 115, respectively. In FIG. 2, 106denotes a brush holder, 109 and 110 brackets, and 111 armature iron.

Referring to FIGS. 2 and 3, two sets of armature windings are arrangedindependently in electrical structure, and the field winding 103 isarranged in common to supply flux to two sets of armature windings 112and 113.

In the embodiment shown in FIG. 1, the battery 9 constitutes the firstvoltage supplier, and the battery 18 constitutes the second voltagesupplier.

When a driver operates the steering wheel 1, the steering shaft 1A isdriven rotatably. The torque caused by the rotational movement of thesteering shaft 1A is detected by the torque detector 3. The detectedsignal is input to the controller 10 from the torque detector 3. Thecontroller 10 inputs the electric power of the battery 9 and supplied itto the motor 11 at a level corresponding to the detected signal, and themotor 11 supplies an auxiliary steering force corresponding to thedetected signal. Since the general load 12, such as the lights, theignition system, etc. is connected to the battery 18, for instance, theintensity of illumination of the head lights is not decreased by theoperation of the motor-driven power steering apparatus. Accordingly, thesafe operation of the automobile is not affected by the operation of themotor-driven power steering apparatus when the automobile is running atnight or through a tunnel.

Since the voltage of the first output terminals 21 is set at a highvoltage level, current flowing through a semiconductor element of thepower steering apparatus connected to the first output terminal 21 canbe reduced so that the semiconductor element can be miniaturized and thecost of manufacture thereof can be reduced. The battery 9 as the voltagesupplier is able to connect to the power steering apparatus by changingthe specification of the armature winding (turn and diameter of winding)of the generator 17, so that the size of the apparatus does not becomelarge and the cost of producing the apparatus can be reduced.

Referring to FIG. 4, a condenser 120 is used in the embodiment as thefirst voltage supplier instead of the battery 9 used in the embodimentof FIG. 1. In the embodiment shown in FIG. 4, the condenser 120 has theeffect of absorbing the noise caused by switching of the semiconductorelement of the controller 10. Other structure, operation and effect ofthe embodiment shown in FIG. 4 is same to that of FIG. 1.

According to the embodiments shown in FIGS. 1 and 4, the power source toother electric parts is not changed; for instance, the intensity of theillumination of the head lights is not reduced by the operation of themotor-driven power steering apparatus. And also, the motor-driven powersteering apparatus can be supplied in small size and low manufacturingcost.

FIG. 5 shows one embodiment of the present invention applied to a rackand pinion system. Referring to FIG. 5, 1 denotes the steering wheel, 23a steering shaft, 24 a middle shaft, 25 a pinion, 7 a rack shaft, 5 asteering gear box, 11 a DC motor in high voltage specification as anactuator for generating an auxiliary steering force, 20 a reducer, 26 apinion for the auxiliary steering force, 20 a reducer, 26 a pinion forthe auxiliary steering force, 10 a torque detector, 10-1 a choppercontroller, 12 electrical devices mounted on the vehicle (load), 13 anengine, 14 and 15 pulleys, 15 a belt, 17 a generator for charging abattery, 18 a battery 10-2 a chopper, and 27 a diode.

When the steering is carried out by turning the steering wheel 1, thegear rack 5 held slidably within the steering gear box 4 is movedthrough the pinion 25 along the axial direction of the gear rack, and atorque is applied to the steering shaft 23, the torque is detected bythe torque detector 3, and a signal is generated corresponding to thetorque. The signals from the torque detector and a steering angle sensor(not shown) are input to the chopper controller 10-1, which outputs acontrol signal to the chopper 10-2 to generate a predetermined torque bycontrolling the power supplied to the motor 11. The torque is applied tothe gear rack 5 through the reducer 20, the pinion 26 and gear box 6.Thereby, an auxiliary steering force is generated in the motor-drivenpower steering apparatus.

FIG. 6 is a circuit diagram of a motor-driven power steering apparatusforming one embodiment of the present invention. Referring to FIG. 6,the chopper 10-2, which is shown as a switching transistor therein, isconnected to the motor 11 in series and is connected directly to the DCoutput (high voltage) of the rectifier 115, which is powered fromgenerator 17 through the lead wire 114. A flywheel diode 28 is connectedacross motor 11. On the other hand, the DC output (low voltage), whichis obtained as an output of the rectifier 117 from the armature winding113 of the generator 17 through the lead wire 116, is connected to thebattery 18 and the load 12 in parallel to supply electrical power tothem, and also is connected to the DC output from rectifier 115 throughthe diode 27 of the blocking inverse current type. Although a controlcircuit is necessary for changing over the rotational direction of themotor 11 reciprocally, the control circuit is not shown in FIG. 6.

The power supply source for driving the motor which generates theauxiliary power steering force, is changed over automatically dependingon the running or stopping of the generator 17 for generating apredetermined electric power, since the diode 27 is provided in theembodiment shown in FIG. 7. Hereunder, we will explain the operation ofthe circuit shown in FIG. 6 referring to FIGS. 7 and 8.

Referring to FIG. 7, the generator 17 generates the voltage V_(B) =48volts via rectifier 115 and the voltage V_(A) =12 volts via rectifier117 with the revolution of the engine 13. The diode 27 is turned OFF byreverse biasing. The rectifier 115 supplies the voltage V_(B) to themotor 11. The chopper 10-2 is operated by the control signal from thechopper controller 10-1 so that the motor 11 is supplied with apredetermined current I₁, to provide a predetermined auxiliary steeringforce. At this time, since the voltage specification of the motor 11 48volts, the current I₁ for generating a required auxiliary steering forceis reduced to 1/4 compared with a conventional motor which is excited by12 volts.

Referring to FIG. 8, the output of rectifier 115 and the output ofrectifier 117 are zero, since the generator 17 is not driven by theengine 13. Therefore, the voltage V_(A) is 12 volts as a result of thebattery 18. At this time, the diode 27 is caused to be forwarded biased.When the chopper 10-2 is operated by the chopper controller 10-1 theelectric power I₂ is supplied to the motor 11 from the battery 18 sothat the motor 11 generates a torque to supply an auxiliary steeringforce. At this time, the motor 11, which has a voltage specification of48 volts, is driven by the voltage of 12 volts supplied from the battery18 so that the response speed of the motor is insufficient. However, themagnitude of the current I₂ can be maintained equivalently to anapproximate same value by changing the duty ratio of the current flowingthrough the chopper provided as transistor 10-2. Consequently, the sameauxiliary steering force can be obtained in case of FIG. 8 as providedin the case of FIG. 7. At this time, there is no problem with thegenerator 17, since reverse current to the generator 17 is blocked bythe rectifiers 115 and 117, as well known.

In the embodiment, the output voltage of the generator 17 is selected tobe 12 volts at the first DC output and 48 volts at the second DC output,respectively. A transistor is used as the chopper in the describedembodiment; however, a gate turn-off transistor, a thyristor, or fieldeffect transistor (FET), etc. can be used instead. Also, the DC motor 11is used as an auxiliary steering force generating actuator. However, theinvention is not limited to use of the DC motor. For instance, an ACmotor such as induction motor, a brushless type motor (synchronousmotor) of a DC motor, or other motors can be used instead. Of course,any other DC motors can be employed without respect to their magneticfield types.

FIG. 9 shows one embodiment of the present invention in which abrushless DC motor is employed as an actuator for generating anauxiliary steering force. In FIG. 9, the same parts as in FIG. 6 areindicated by the same reference symbols. The difference between FIG. 9and the previous embodiment in FIG. 6 is that the second DC output B,namely an output of high voltage, is connected to the synchronousbrushless DC motor 11 through an invertor 50; and common earth wires ofthe inverse current blocking diode 27 and the high and low voltagerectifiers are equipped between the invertor 50 and the rectifier 115.

In the embodiment shown in FIG. 9, the chopper can be omitted, and thebrushless DC motor can be operated by the high voltage rectifier 115during running of the engine and by the battery 18 when the engine isnot running. Incidentally, the motor 11 can be an induction motor,instead.

In the embodiments, the motor of the motor-driven power steering isconnected as a high voltage load. The present invention is not limitedthereto. For instance, when an ignition system is connected to the highvoltage rectifier 115, it can resolve a drawback that the voltage of theignition device is not increased based on a short ignition duration whenan automobile is running at a high speed. Further, when all of thegeneral motors, such as the car cooler motor, are connected to the highvoltage side of the generator, the motor current can be reduced.

According to the embodiments shown in FIGS. 5 and 9, the choppingtransistor and the motor can be driven by high voltage when the engineis running, and the current flowing through the motor can be reduced inproportion to the magnitude of a reciprocal of a ratio of the highvoltage to the low voltage of the generator 17. Since the general loadand the control apparatus are driven by the low voltage battery which isequipped separately from the high voltage battery used for themotor-driven power steering, the intensity of the light is not reducedwhen the automobile is driven at night.

Since the apparatus shown in FIG. 9 does not need the build-up choppershown in FIG. 6, it has a long durability and becomes a compact system.

According to the embodiments shown in FIGS. 6 and 9, since themotor-driven power steering motor can be driven by low current when theengine is not running, the power steering can be driven when theautomobile is transported by a wrecker truck in the event of an enginefailure.

In the embodiments of FIGS. 1, 4 and 5, the present invention is appliedto the motor-driven power steering apparatus. However, the presentinvention also can be applied to a motor-driven oil pressure type powersteering apparatus.

What we claim is:
 1. A motor driven power steering apparatus for avehicle which depends on a DC power source as an energy source forelectrical devices mounted on the vehicle having a steering shaft,comprising:a generator driven by an engine of the vehicle, saidgenerator having first winding means for generating a first DC voltagehaving a first voltage level and second winding means for generating asecond DC voltage having a second voltage level which is higher thansaid first voltage level; first and second voltage suppliers connectedto said first and second winding means, respectively; and actuator meansfor generating an auxiliary steering force for the vehicle, including amotor for providing an auxiliary steering force, torque detector meansfor detecting a torque applied to the steering shaft of the vehicle andcurrent control means connected between said second voltage supplier andsaid motor for controlling a current supplied to said motor to controlsaid auxiliary steering force in response to said torque detector means,said first voltage supplier being connected to supply voltage to otherelectrical devices of the vehicle.
 2. An apparatus according to claim 1,wherein said generator includes a field winding connected to receive anexcitation voltage from said first winding means and to supply flux toboth said first and second winding means.
 3. An apparatus according toclaim 1, wherein said first and second voltage suppliers are batteries.4. An apparatus according to claim 1, wherein said first voltagesupplier is a battery and said second voltage supplier is a condenser.